The present invention generally pertains to electronic communications systems and is particularly directed to an improvement to frequency synthesizers of the type that include a voltage controlled oscillator (VCO).
In frequency synthesizers of the type that include a VCO, the VCO produces a VCO output signal at a predetermined frequency in response to an analog VCO control signal. In one of the VCO type of frequency synthesizer, the analog VCO control signal is generated by a phase-locked loop circuit in which an input signal is phase locked to a reference signal at the predetermined frequency. In another of the VCO type of frequency synthesizer, the analog VCO control signal is generated by a charge pump circuit which supplements or decreases the voltage of the analog VCO control signal in response to an error signal produced by comparing a reference value that is representative of the predetermined frequency with a measurement value representative of the measured frequency of the VCO output signal. The measurement value typically is produced by scaling the measured frequency of the VCO output signal to a proportionately lower frequency.